Saturday, 13 June, 2009 15:59
Written by Ray Shore
So you know the basics of imaging the planets with an astrophotography webcam. You have mastered the process of capturing the AVI, running it through Registax, and cleaning it up in Photoshop. But how do you tease out that extra bit of detail that separates your photos from all the rest you have ever taken? AstroPhotography Tonight will show you how to make a difference with 5 important steps. Master these and you will step up to the next level in webcam astrophotography!
1. Telescope Collimation
Precise telescope mirror alignment is crucial for imaging the planets at high power. It can make the difference between a razor sharp planetary image and a big blob that vaguely resembles a pancake, er, planet! This is a common problem for webcam imagers because they haven’t verified exact mirror alignment before they start imaging. It is understandable why imagers are shy about tampering with the mirror adjustment screws since it is a bit tricky. But take some time to learn how to collimate your particular telescope and you will reap the rewards!
Saturn Before Collimation
Saturn After Collimation
2. Image During the Best Seeing Conditions
Take advantage of the best seeing conditions. You want to image during good stable skies. When there is a high amount of turbulence and temperature differences in the atmosphere, the seeing will be poor. It is frustrating to image when the seeing conditions are sub-par. The planet will look as if you are trying to image it through rippling water. This moon video demonstrates the effects of turbulence:
There are several indicators that will help you determine if the skies will be in your favor for webcam astrophotography of the planets:
Clear Sky Chart
The Clear Sky Chart (provided by A. Danko) is an awesome tool for checking the upcoming sky conditions for your area. It makes predictions about various conditions such as cloud cover, transparency, seeing, and darkness that will occur within the next 48 hours. The forecast data is generated by Meteorological Services of Canada. Of particular importance for webcam astrophotography of planets is the “seeing” forecast. Dark blue blocks for the line labeled ”seeing” usually indicates that stable skies are predicted. Be sure to read through the information on the sky clock page to get familiar with reading the chart.
The Stars Are Twinkling
If the stars are twinkling rapidly, this is a good indication that your night of webcam imaging of the planets will end in utter disappointment. The stars twinkle due to very turbulent air. And turbulence is a planetary astrophotographers worst enemy. Wait until the stars become steady then take advantage of this favorable condition!
Red Sunset, Poor Conditions for High Power Astrophotography
“Red sky at sunset, webcam imagers upset”. This should be the saying for us planetary imager types! A red sky (and sun) may indicate that the atmosphere is loaded with dust and moisture particles. The sky appears red due to the red wavelengths making their way through the particles in the atmosphere. Note that we mostly see red because the blue wavelengths do not reach us. They are scattered instead. Anyway, lots of dust and moisture in the atmosphere can limit the opportunity for recording highly detailed images of the planets. Look for sunsets where the sky and sun stay more on the yellow side than red.
High Pressure System/Jet Stream
An indication of good seeing conditions is whether you have a stable air mass above you. In his book, Lunar and Planetary Webcam User’s Guide, Martin Mobberley goes into great detail about how important a stable high pressure system and the jet stream are to webcam astrophotography of the planets. In fact, he considers the jet stream to be the “fine planetary detail wrecker”.It is beyond the scope of this article, but Mobberly will teach you the important things to check when it comes to atmospheric stability. In fact, he shows you how to monitor the jet stream for the ideal imaging conditions. Packed full of excellent information for planetary imaging, AstroPhotography Tonight highly recommends this book.
Final Message Regarding Seeing Conditions
Seeing is a very important factor in producing good resolution images of the planets. The best astrophotographers in the world only image when the sky conditions are favorable. It takes some patience waiting for the right time to image the planets. And don’t be surprised if the seeing conditions change from night to night and even hour to hour. When it happens though, you want to be ready with your telescope and webcam so you don’t miss that special moment when sky opens up with crystal clear seeing! This very point leads many astrophotographers to build an observatory (like this one) so that they will be ready to image at a moments notice.
3. Thermal Equilibrium
Set your scope up outside at least 1 hour before imaging. If it hasn’t had time to reach thermal equilibrium with the outdoor temperature, the image will become distorted as the heat escapes the tube. This can take a long time in large closed systems such as SCT’s and Maks where the air is trapped. AstroPhotography Tonight has discovered an interesting device for ventilating the insides of these types of scopes. It’s called the CosmicOne SCT cooler by Lymax (no affiliation with AstroPhotography Tonight).
CosmicOne SCT Cooler
Many astrophotographers now use fans to cool down the primary mirror in order to allow more time for imaging and produce better results. Reaching thermal equilibrium before webcam astrophotography begins can make a huge difference in the amount of detail that can be captured.
4. Critical Focus
Tweak the focus until you get the sharpest image possible “overall”. The planet will appear to go in and out of focus constantly. This is due to an unstable atmosphere that you are imaging through. Spend a lot of time tweaking the focusing knob until you achieve the best possible results. Then it is up to the webcam to freeze the best frames in the sequence for stacking in a program such as Registax later. See Ray Shore’s Webcam Astrophotography Tutorial for Planets.
Various methods for achieving critical focus:
Note about telescope masks: astrophotographers are turning to these masks as an aid for achieving critical focus without the hassle of endless tweaking and guesswork. Masks like the AstroZap shown below make it easy to determine if the optics have slight inside focus, outside focus, and most importantly, perfect focus.
AstroZap Focusing Caps
5. Image when the Planet is High in the Sky
The closer the planet is to the horizon, the more turbulent air you are trying to image through. Thus, the best possible time to turn your telescope and webcam on the planet is when it is at or near the zenith (point directly above you).
Additional Tips and Comments Welcome
If you have more good tips on planetary webcam astrophotography, please add them in the comments section below. AstroPhotography Tonight welcomes all input that will help those that are looking to enhance their skills.
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I decided to mount the ED80 directly to the CGEM saddle plate. I had the ADM dovetail rings and adapter set already (previously used to piggyback the ED80 to the LX200 SCT) so it was a matter of purchasing the DMM7 from ADM. This allows me to mount the ED80 to the CGEM saddle plate. 
I’m also hearing a lot about Bahtinov focusing masks. Some imagers are making these masks themselves but a professionally made one is very reasonable. In fact, it was only $14.95 for the Bahtinov mask for my ED80 at telescopes.com. These masks allow fast and easy critical focus. It’s simply a matter of adjusting focus until a symmetrical diffraction spike pattern is obtained. 
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